1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a gate driver, a liquid crystal display device and a driving method thereof capable of preventing a crosstalk.
2. Description of the Related Art
Liquid crystal display devices (LCD) have a number of advantages, such as a low voltage driving signal, a low power consumption, a slim profile, light weight, and full color reproduction. LCDs are widely used as display windows of watches and calculators, computer monitors, television (TV) sets, TV monitors, and mobile telephones.
In the LCD device, liquid crystals are injected into a liquid crystal panel and controlled to selectively transmit a light emitted from a light source. In this manner, predetermined images are displayed.
However, crosstalk causing an abnormal display characteristic occurs when the LCD is driven. The crosstalk is a phenomenon that when white data or black data is concentrated on a specific liquid crystal cell, original gray-scale levels of liquid crystal cells adjacent to that specific liquid crystal cell in four directions are influenced by the gray-scale level of the specific liquid crystal cell, so that different gray-scale levels are displayed. Vertical crosstalk occurs in the liquid crystal cells disposed up and down from the specific liquid crystal cell, and horizontal crosstalk occurs in the liquid crystal cells disposed to the right and left of the specific liquid crystal cell. The vertical crosstalk occurs when the TFTs are not sufficiently electrically turned off. That is, vertical crosstalk occurs when unintended gray-scale voltages are transmitted through the TFTs that are not sufficiently electrically turned off. The horizontal crosstalk occurs due to variations in the potential of the common electrode. That is, when the gray-scale voltage is charged to liquid crystal cells adjacent in the horizontal direction to an arbitrary liquid crystal cell, an accurate gray-scale level is not supplied to an arbitrary liquid crystal cell due to an influence of the potential of the common electrode, resulting in the horizontal crosstalk.
FIG. 1A is an ideal operation waveform of an LCD, and FIG. 1B is an actual operation waveform of an LCD.
Referring to FIG. 1A, in an ideal state, there are no stray capacitance of the TFT (that is, a parasitic capacitance between a source terminal and a drain terminal, a parasitic capacitance between a source terminal and a gate terminal, and a parasitic capacitance between a gate terminal and a drain terminal), no parasitic capacitance between a source terminal and a gate terminal, and no parasitic capacitance between a gate terminal and a gate line adjacent thereto. Also, a common voltage supplied to a common electrode is constantly maintained by a direct current (DC).
Accordingly, the TFTs are turned on at a transition from a low-potential gate voltage Voff to a high-potential gate voltage Von. Then, data voltages are charged to the respective pixels through data lines and TFTs. Also, the TFTs are turned off at a transition from the high-potential gate voltage Von to the low-potential gate voltage Voff, and the charged voltages of the pixels are maintained as the data voltages. In this case, the data voltages supplied to the pixels are identical to the pixel voltages Vpixel applied to the pixels. Thus, there exists no stray capacitance at the ideal state and the common voltage is not changed, such that the crosstalk does not occur.
In actual practice, however, stray capacitance does exist in the TFT. Also, the common voltage supplied to the common electrode is changed.
In such a case, as shown in FIG. 1B, an unintended stray capacitance occurs in the TFT at a transition from a high-potential gate voltage Von to a low-potential gate voltage Voff. Due to the stray capacitance, a distortion occurs in the common voltage Vcom and the low-potential gate voltage Voff. Due to the distortion in the common voltage and the low-potential gate voltage, the data voltages supplied to the pixels are dropped and the decreased pixel voltages Vpixel are charged to the pixels. Thus, the crosstalk is caused by the decreased pixel voltages Vpixel.
In general, an intensity of the crosstalk is largely dependent of the variations in the common voltage and the low-potential gate voltage. A technology for maximally suppressing the variation of the common voltage so as to prevent the crosstalk is widely used.
As described above, however, the crosstalk is sensitive to the variation in the low-potential gate voltage as well as the variation in the common voltage. Therefore, even though the variation in the common voltage is suppressed, the crosstalk cannot be completely prevented. A method capable of preventing the crosstalk by suppressing the variation in the low-potential gate voltage has not been proposed in the related art. Accordingly, there is a demand for a method capable of preventing crosstalk by controlling the variation in the low-potential gate voltage.